Advancements continue to be made in wireless communications technology. For example, wireless local area networks (WLANs) and wireless personal area networks (WPANs) networks are becoming more common in homes and businesses. Such networks may include a variety of independent wireless electronic devices or terminals, which wirelessly communicate with one another. WLANs and WPANs may operate according to a number of different available standards, including IEEE standards 802.11 (Wi-Fi), 802.15 (Bluetooth) and 802.16 (WiMax), as well as the WiMedia Alliance Ultra-Wideband (UWB) standard.
FIG. 1 is a block diagram showing a conventional wireless network 100, including multiple terminals configured to communicate with one another over exemplary WPAN 125. The wireless terminals may include any electronic devices or nodes configured to communicate with one another. For example, FIG. 1 depicts a home network in which the electronic devices include a personal computer 120, a digital television set 121, a digital camera 122 and a personal digital assistant (PDA) 123. The network 100 may also include an interface to other networks, such as modem 130, to provide connectivity of all or some of the wireless devices 120-123 to the Internet 140, for example. Of course, there are many other types of wireless networks in which electronic devices communicate with one anther, including networks in manufacturing plants, medical facilities, security systems, and the like.
Wireless devices may communicate with one another using directional antennas, which extend transmission range. For example, recent wireless networks operate in very high frequency bands (e.g., 60 GHz), and thus use directional antennas to compensate for high path loss associated with high frequency bands. In both centralized and distributed wireless networks, wireless devices using directional antennas must align their respective antennas at the same time in order to communicate. In other words, the wireless devices must first find each other, which is accomplished by the wireless devices scanning (e.g., sweeping their antenna beams) around surrounding areas. However, the wireless devices may not discover one another unless there is pre-coordination among them to assure that they are sweeping their antenna beams at the same time.
Beacons are widely used to convey important control information between devices. Beacons are usually broadcast so that all devices in the transmission range of the beaconing device can receive the beacons. For example, an IEEE 802.11 access point periodically sends out beacons so that the IEEE 802.11 wireless devices around the access point can associate with the access point and communicate. As stated above, in wireless networks in which directional antennas are used, beacons may only be sent in certain directions. As a result, only a limited number of devices in proximity of the beaconing device will receive the beacons, thus making beacons less useful. The wireless devices may be pre-programmed to know the direction of each other's antennas, but this requires a protocol to coordinate the wireless devises' antenna directivity, as well as beacon transmission, reception and processing.
In other words, wireless devices may not be able to discover and communicate with each other even though they are in the same network 100 and in proximity to one another. Such coordination or synchronization is difficult and costly to implement. However, wireless devices not having a common time-domain reference point for coordinating antenna control and/or beacon transmission will not communicate properly as a network.
Accordingly, it would be desirable to provide a wireless device and method of wireless communications that provides a mechanism enabling wireless devices to find and communicate with each other, particularly when the wireless devices are using directional antenna systems.
In one aspect of the invention, a method is provided for discovering hidden wireless devices in a wireless network using a directional antenna system, preventing partitioning of the wireless network. The method includes joining a first wireless device located in a first antenna sector in response to an initial first beacon received from the first wireless device; receiving multiple first beacons from the joined first wireless device during corresponding first beacon periods; and scanning at least a second antenna sector during at least one first beacon period of the first beacon periods to listen for second beacons from a second wireless device in the second antenna sector, while remaining joined with the first wireless device. The first beacons are not received while at least the second antenna sector is scanned.
The method may further include sending multiple first response beacons to the joined first wireless device in response the received first beacons. The first response beacons are not sent while scanning at least the second antenna sector.
The method may further include receiving an initial second beacon from the second wireless device while scanning the second antenna sector; joining the second wireless device in response to the initial second beacon; and receiving multiple second beacons from the joined second wireless device during corresponding second beacon periods. At least a portion of the first beacons continues to be received.
When the first beacon periods occur at different times than the second beacon periods, the method may further include receiving each of the first beacons and the second beacons. When the first beacon periods occur at the same times as the second beacon periods, the method may further include alternating between receiving the first beacons and the second beacons.
The method may further include sending multiple second response beacons to the joined second wireless device in response the received second beacons. When sending the first response beacons occurs at the same times as the second beacon periods, the method may further include alternating between sending the first response beacons and receiving the second beacons. When sending the second response beacons occurs at the same times as the first beacon periods, the method may further include alternating between sending the second response beacons and receiving the first beacons.
The method may further include scanning at least a third antenna sector during one first beacon period of the multiple first beacon periods and one second beacon period of the multiple second beacon periods to listen for third primary beacons, while remaining joined with the first wireless device and the second wireless device. The first beacons and the second beacons may not be received while the third antenna sector is being scanned. Scanning the second antenna sector may include sweeping a beam of the directional antenna system.
In accordance with a representative embodiment, an apparatus is provided for communicating with multiple wireless devices through a wireless network, where the apparatus is initially joined with a first wireless device located in a first antenna sector of multiple antenna sectors. The apparatus includes a directional antenna system, a transceiver and a processor. The directional antenna system is configured to communicate over the wireless network in the antenna sectors. The transceiver is configured to receive multiple first beacons from the joined first wireless device via the antenna system during corresponding first beacon periods. The processor is configured to control the antenna system to scan at least a second antenna sector of the antenna sectors during at least one first beacon period of the first beacon periods to listen for beacons from the wireless devices. The first beacons are not received while the directional antenna system is scanning, and the apparatus remains joined with the first wireless device.
The transceiver may receive an initial second beacon from a second wireless device located in the second antenna sector while the antenna system is scanning, enabling the apparatus to join with the second wireless device. The transceiver may also receive multiple second beacons from the joined second wireless device during corresponding second beacon periods, while continuing to receive at least a portion of the first primary beacons. The antenna system may include one of an antenna array or a steerable antenna.
When the first beacon periods occur at different times than the second beacon periods, the transceiver may receive each of the first primary beacons and the second primary beacons. When the first beacon periods occur at the same times as the second beacon periods, the transceiver may alternate between receiving the first primary beacons and the second primary beacons.
The transceiver may send multiple first response beacons to the joined first wireless device in response the received first beacons and send multiple second response beacons to the joined second wireless device in response the received second beacons. The first response beacons may not be sent while the antenna system scans the antenna sectors. When sending the first response beacons occurs at the same times as the second beacon periods, the transceiver may alternate between sending the first response beacons and receiving the second beacons. When sending the second response beacons occurs at the same times as the first beacon periods, the transceiver may alternate between sending the second response beacons and receiving the first beacons.
In accordance with a representative embodiment, a method is provided for enabling a secondary wireless device to discover multiple primary wireless devices through a wireless network, where activation schedules of the secondary wireless device and the primary wireless devices are not synchronized. The method includes receiving first primary beacons from a first primary wireless device in a first antenna sector and sending first secondary beacons to the first primary wireless device in response; skipping receiving the first primary beacons from the first primary wireless device; and scanning other antenna sectors and listening for additional primary beacons while skipping receiving the first primary beacons. The method also includes receiving an initial second primary beacon from a second primary wireless device in a second antenna sector while scanning the antenna sectors and sending an initial second secondary beacon to the second primary wireless device in response; and receiving second primary beacons from the second primary wireless device and sending secondary beacons to the second primary wireless device in response, in addition to receiving the first primary beacons from a first primary wireless device and sending the first secondary beacons to the first primary wireless device in response.
The first primary beacons may be received during a first time period and the second primary beacons may be received during a second time period. When the first time period conflicts with the second time period, the method further includes alternating receiving the first primary beacons and the second primary beacons.